Systems for reducing startup emissions in power plant including gas turbine

ABSTRACT

Embodiments of emission reduction system including various embodiments of an emission filters for a power plant including a gas turbine are disclosed. The system includes: an emission filter; and a retraction system operably coupled to an exhaust passage of the gas turbine. The exhaust passage defines an exhaust path of exhaust from the gas turbine. The retraction system selectively moves the emission filter between a first location within the exhaust path and a second location out of the exhaust path. In a combined cycle power plant, the first location is upstream of a heat recovery steam generator (HRSG). The systems and filters described allow for temporary positioning of emission filter(s) just downstream of a gas turbine exhaust outlet, or upstream of an HRSG, where provided, for emission reduction at low loads or startup conditions, and removal of the emission filter(s) once operations move to higher loads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. Nos. 15/437,771,15/437,780, 15/437,785, and 15/437,794, filed concurrently and currentlypending.

BACKGROUND OF THE INVENTION

The disclosure relates generally to power plants, and more particularly,to a system for reducing startup emissions in a power plant including agas turbine.

Gas turbine systems are widely used to generate power. Combined cyclepower plants employ a gas turbine system and a steam turbine system togenerate power. As gas turbine systems and combined cycle power plantshave progressed, power plants using the systems have had increasingoperational demands placed upon them. In particular, power plants havebeen required to remain operational over a larger load spectrum whilealso meeting environmental regulations. One challenge relating to gasturbine system operation is meeting environmental regulations, e.g.,nitrogen dioxide (NOx) and/or carbon monoxide (CO) limitations, duringlow load operations such as during startup of the system. For example,some environmental regulations require NOx emissions to be as low as 19kilograms/hour during start up emissions, which is increasinglydifficult with larger gas turbine systems. During the start-up of thegas turbine system, a number of operational characteristics create highNOx and CO emissions. For example, in a combined cycle power plant, gasturbine system exhaust may be at about 370° Celsius at startup(approximately 5-20% load) to allow heat recovery steam generator (HRSG)warmup (traditional thermal stress mitigation), mating of steamtemperature matching for steam turbine system start, reheat pressurereduction for steam turbine system start (HP turbine section) and gasturbine system fuel heating.

During normal higher load operation, emissions from a gas turbine systemare typically controlled by two emission control systems. First, aselective catalytic reduction (SCR) system converts NOx to nitrogen,water and carbon dioxide (CO₂) by causing the exhaust to react with areducing agent, e.g., anhydrous ammonia, aqueous ammonia or urea.Second, the exhaust may be passed through a CO catalyst system to removeCO. However, during low load conditions of a combined cycle power plant,for example, the SCR system and the CO catalyst system are not activebecause they do not attain the desired operating temperature becausethey are located after any heat exchanger capable of creating therequired heat, e.g., a superheater within the HRSG or a high pressure(HP) drum. For example, at startup it can take more than 30 minutes forthe traditional emission control systems to reach sufficient operatingtemperatures to start reducing NOx and CO emissions. In this case,exhaust exits to atmosphere from the HRSG without emission control.During this initial period, the power plant may continue to emit NOx andCO emissions which are counted against the government issued permitlimits for startup and overall yearly tons. This issue can end upputting restrictions on the power plant operability such as limitationson the number of starts and total hours of operation in a year. In orderto address CO emissions, additional CO catalysts have been positionedupstream of a superheater, but such structure places further limitationson the power plant during full load operation. In another approach, theload of the gas turbine system is quickly raised from startup to a pointwhere emissions are lower (referred to as ‘rapid response’). However,this approach adds more equipment and complex control systems to thepower plant.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides an emission reduction systemfor a power plant including a gas turbine, the system comprising: anemission filter; and a retraction system operably coupled to an exhaustpassage of the gas turbine, the exhaust passage defining an exhaust pathof exhaust from the gas turbine, the retraction system selectivelymoving the emission filter between a first location within the exhaustpath and a second location out of the exhaust path.

A second aspect of the disclosure provides a method of reducingemissions for a power plant including a gas turbine, the methodcomprising: providing an emission filter operably coupled to aretraction system that is operably coupled to an exhaust passage of thegas turbine, the exhaust passage defining an exhaust path of exhaustfrom the gas turbine; and selectively moving the emission filter, usingthe retraction system, between a first location within the exhaust pathand a second location out of the exhaust path in response to an emissioncondition of the exhaust from the gas turbine.

A third aspect of the disclosure provides an emission reduction systemfor a power plant including a gas turbine, the system comprising: anemission filter including a first panel and a second panel, each panelincluding an open structure frame having a filter medium therein throughwhich exhaust passes to remove an exhaust component of an exhaust of thegas turbine; and a retraction system operably coupled to an exhaustpassage of the gas turbine, the exhaust passage defining an exhaust pathof the exhaust from the gas turbine, the retraction system selectivelylaterally moving each of the first and second panels between a firstlocation within the exhaust path within the exhaust passage and a secondlocation out of the exhaust path.

A fourth aspect of the disclosure provides an emission reduction systemfor a power plant including a gas turbine, the system comprising: anemission filter including an open structure frame having a filter mediumtherein through which exhaust passes to remove an exhaust component ofan exhaust of the gas turbine; and a retraction system operably coupledto an exhaust passage of the gas turbine, the exhaust passage definingan exhaust path of the exhaust from the gas turbine, the retractionsystem selectively vertically moving the emission filter through anopening in an upper wall of the exhaust passage between a first locationwithin the exhaust path within the exhaust passage and a second locationout of the exhaust path.

A fifth aspect of the disclosure provides an emission reduction systemfor a power plant including a gas turbine, the system comprising: acarbon monoxide (CO) catalyst filter through which exhaust passes toremove carbon monoxide from an exhaust of the gas turbine, the COcatalyst filter positioned upstream of a heat recover steam generator(HRSG) operably coupled to the exhaust passage of the gas turbine forgenerating steam for a steam turbine; and a retraction system operablycoupled to an exhaust passage of the gas turbine, the exhaust passagedefining an exhaust path of the exhaust from the gas turbine, theretraction system selectively moving the CO catalyst filter between afirst location within the exhaust path within the exhaust passage and asecond location out of the exhaust path.

A sixth aspect of the disclosure provides an emission filter for a powerplant including a gas turbine, the emission filter comprising: a seriesof pivotally coupled panels, each panel including an open structureframe having a filter medium therein through which exhaust passes toremove an exhaust component of an exhaust of the gas turbine.

A seventh aspect of the disclosure provides an emission reduction systemfor a power plant including a gas turbine, the system comprising: anemission filter including a series of pivotally coupled panels, eachpanel including an open structure frame having an open structure framehaving a filter medium therein therein through which the exhaust passesand a pair of opposing bearings extending from opposing ends of therespective panel; and a retraction system operably coupled to an exhaustpassage of the gas turbine, the exhaust passage defining an exhaust pathof exhaust from the gas turbine, the retraction system selectivelymoving the emission filter between a first location within the exhaustpath and a second location out of the exhaust path.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIG. 1 shows a schematic diagram of an illustrative, conventionalcombined cycle power plant.

FIG. 2 shows a cross-sectional view of an illustrative, conventional gasturbine system.

FIG. 3 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 4 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 5 shows a perspective view of an emission filter and retractionsystem according to an embodiment of the disclosure.

FIG. 6 shows a perspective view of an emission filter and retractionsystem according to another embodiment of the disclosure.

FIG. 7 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 8 shows a cross-sectional view of part of an emission reductionsystem according to another embodiment of the disclosure.

FIG. 9 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 10 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 11 shows a schematic, perspective view of part of an emissionreduction system according to an embodiment of the disclosure.

FIG. 12 shows a schematic, perspective view of part of an emissionreduction system according to an embodiment of the disclosure.

FIG. 13 shows a schematic, perspective view of part of an emissionreduction system according to an embodiment of the disclosure.

FIG. 14 shows a perspective view of a retraction system according to anembodiment of the disclosure.

FIG. 15 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 16 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 17 shows a cross-sectional view of a retraction system according toan embodiment of the disclosure.

FIG. 18 shows a cross-sectional view of a retraction system according toanother embodiment of the disclosure.

FIG. 19 shows a cross-sectional view of part of an emission reductionsystem according to an embodiment of the disclosure.

FIG. 20 shows a cross-sectional view of part of an emission reductionsystem according to another embodiment of the disclosure.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As an initial matter, in order to clearly describe the currentdisclosure it will become necessary to select certain terminology whenreferring to and describing relevant machine components within combinedcycle power plant, gas turbine system and/or a heat recover steamgenerator. When doing this, if possible, common industry terminologywill be used and employed in a manner consistent with its acceptedmeaning. Unless otherwise stated, such terminology should be given abroad interpretation consistent with the context of the presentapplication and the scope of the appended claims. Those of ordinaryskill in the art will appreciate that often a particular component maybe referred to using several different or overlapping terms. What may bedescribed herein as being a single part may include and be referenced inanother context as consisting of multiple components. Alternatively,what may be described herein as including multiple components may bereferred to elsewhere as a single part.

In addition, several descriptive terms may be used regularly herein, andit should prove helpful to define these terms at the onset of thissection. These terms and their definitions, unless stated otherwise, areas follows. As used herein, “downstream” and “upstream” are terms thatindicate a direction relative to the flow of a fluid, such as theworking fluid through the turbine engine or, for example, the flow ofexhaust through a heat recover steam generator. The term “downstream”corresponds to the direction of flow of the fluid, and the term“upstream” refers to the direction opposite to the flow. The terms“forward” and “aft,” without any further specificity, refer todirections, with “forward” referring to the front or compressor end ofthe engine, and “aft” referring to the rearward or turbine end of theengine or HRSG end of the exhaust path. The term “axial” refers tomovement or position parallel to an axis.

The disclosure provides emission reduction systems and filters thatallow for temporary positioning of emission filter(s) just downstream ofa gas turbine exhaust outlet, or upstream of an HRSG, where provided,for emission reduction at low loads or startup conditions, and removalof the emission filter(s) from the exhaust path once exhaust conditionschange, e.g., due to operations moving to higher loads. For purposes ofdescription, embodiments of the emission reduction systems and filterswill be described relative to a combined cycle power plant. As will beapparent, the teachings of the disclosure are also applicable to anycombustion system such as a gas turbine system.

Turning to FIG. 1, a schematic view of portions of an illustrative,conventional combined cycle power plant 10 is shown. In the instantexample, the power generating system is a single shaft system with twogenerators, but one with skill in the art will readily understand thatthe teachings of the disclosure are applicable to any variety ofcombined cycle power plant. Combined cycle power plant 10 may include agas turbine system 12 operably connected to a generator 14, and a steamturbine system 16 operably coupled to another generator 18. Generator 14and gas turbine system 12 may be mechanically coupled by a shaft 20,which may transfer energy between a drive shaft (not shown) of gasturbine system 12 and generator 14. Also shown in FIG. 1, a heat recoversteam generator (HRSG) 22 is operably connected to gas turbine system 12and steam turbine system 16. HRSG 22 may be fluidly connected to bothgas turbine system 12 and steam turbine system 16 via conventionalconduits (numbering omitted). It is understood that generators 14, 18and shaft 20 may be of any size or type known in the art and may differdepending upon their application or the system to which they areconnected. Common numbering of the generators and shafts is for clarityand does not necessarily suggest these generators or shafts areidentical.

As shown in the cross-sectional view of FIG. 2, a conventional gasturbine system 12 may include a compressor 30 and a combustor 32.Combustor 32 includes a combustion region 34 and a fuel nozzle assembly36. Gas turbine system 12 also includes a gas turbine 38 coupled tocommon compressor/turbine shaft 20. In one embodiment, gas turbinesystem 12 is a MS7001FB engine, sometimes referred to as a 9FB engine,commercially available from General Electric Company, Greenville, S.C.The present disclosure is not limited to any one particular gas turbinesystem and may be implanted in connection with other engines. Inoperation, air enters the inlet of compressor 30, is compressed and thendischarged to combustor 32 where fuel, heated according to embodimentsof the disclosure, such as a gas, e.g., natural gas, or a fluid, e.g.,oil, is burned to provide high energy combustion gases which drive gasturbine 38. In gas turbine 38, the energy of the hot gases is convertedinto work, some of which is used to drive compressor 30 through rotatingshaft 20, with the remainder available for useful work to drive a loadsuch as generator 14 via shaft 20 for producing electricity.

Returning to FIG. 1, the energy in the exhaust gases (dashed line)exiting gas turbine system 12 is converted into additional useful work.The exhaust gases enter HRSG 22 (heat exchanger) in which water isconverted to steam in the manner of a boiler. Within HRSG 22, asuperheater 24 may be provided to superheat the steam using the exhaustand/or another heat source prior to steam turbine system 16, e.g., ahigh pressure (HP) turbine thereof. Steam turbine system 16 may includeone or more steam turbines, e.g., a high pressure (HP) turbine, anintermediate pressure (IP) turbine and a low pressure (LP) turbine, eachof which are coupled to shaft 20. Each steam turbine includes aplurality of rotating blades (not shown) mechanically coupled to shaft20. In operation, steam from various parts of HRSG 22 enters an inlet ofat least one of the steam turbine(s), and is channeled to impart a forceon blades thereof causing shaft 20 to rotate. As will be understood,steam from an upstream turbine may be employed later in a downstreamturbine. The steam thus produced by HRSG 22 drives at least a part ofsteam turbine system 16 in which additional work is extracted to driveshaft 20 and an additional load such as second generator 18, in turn,produces additional electric power. A conventional power plant controlsystem 26 may control the above-described components.

As noted, as combined cycle power plants have progressed, the overallsystems have had increasing operational demands placed upon them. Inparticular, combined cycle power plants have been required to remainoperational over a larger load spectrum while also meeting environmentalregulations, which creates a challenge relating to gas turbine systemoperation in meeting environmental regulations, e.g., nitrogen dioxide(NOx) and/or carbon monoxide (CO) limitations, during low loadoperations such as during startup of the system. In particular, duringthe start-up of the gas turbine system, a number of operationalcharacteristics create relatively high NOx and CO emissions. In oneexample, gas turbine system exhaust may be at about 370° C. at startup(approximately 5-20% load) to allow HRSG warmup (traditional thermalstress mitigation), mating of steam temperature with an ideal for steamturbine system start, reheat pressure reduction for steam turbine systemstart (HP turbine section) and gas turbine system fuel heating.

During normal higher load operation, emissions are typically controlledin a gas turbine system by two emission control systems. First, as shownin the prior art system of FIG. 1, the exhaust may be passed through aCO catalyst system 40 within HRSG 22 to remove CO. Second, a selectivecatalytic reduction (SCR) system 42 within HRSG 22 converts NOx tonitrogen and water by causing the exhaust (dashed line) to react with areducing agent, e.g., anhydrous ammonia, aqueous ammonia or urea. System40 and 42 may be interspersed within various heat transfer piping setsof HRSG 22. During low load conditions, SCR system 42 and CO catalystsystem 40 are not active because they do not attain the desiredoperating temperature, for example, because they are located aftersuperheater 24 (FIG. 1) or an HP drum (not shown). For example, atstartup it can take more than 30 minutes for the traditional systems 40,42 to reach sufficient operating temperatures to start reducing NOx andCO emissions. In this case, exhaust may exit to atmosphere from HRSG 22(dotted line) without emission control. During this initial period,power plant 10 may continue to emit NOx and CO emissions which arecounted against the permit limits for startup and overall yearly tonslimit.

Embodiments of the disclosure provide emission reduction systems andmethods that employ an emission filter(s) that is/are immediately aftergas turbine system and upstream of any HRSG. The emission reductionsystems use a retraction system for selectively moving the emissionfilter from a first location within an exhaust path and a secondlocation outside of the exhaust path. The emission filter(s) can thus beemployed in the first location upstream of the HRSG at which sufficienttemperatures are reached for use of the emission filter(s) duringstartup or other low load conditions, and can be retracted out of theexhaust path during higher loads at which temperatures are too high andduring which use of the emission filter(s) may lead to undesirableexhaust flow restrictions. The teachings of the disclosure will bedescribed as applied to a combined cycle power plant, but may beapplicable to gas turbine systems alone.

FIG. 3 shows a cross-sectional view of a portion of a combined cyclepower plant 110 including a gas turbine system 112 operatively coupledto an HRSG 122, according to one embodiment. Gas turbine system 112 mayinclude any combustion-based turbine system, as described herein. Gasturbine system 112 may also include a conventional duct burner 114downstream of a turbine 116 thereof that burns any residual fuel in anexhaust 118 exiting turbine 116. As understood, exhaust 118 includes avariety of combustion exhaust such as carbon dioxide, carbon monoxide(CO), nitrogen oxide (NOx), etc. Exhaust 118 passes through an exhaustpassage 120 operatively coupled to gas turbine 116 and configured todirect exhaust 118 downstream of gas turbine 116, e.g., to HRSG 122.Exhaust passage 120 may be an integral part of HRSG 122, or may be aseparate passage upstream but operatively coupled to HRSG 122. In anyevent, exhaust passage 120 defines an exhaust path through which exhaust118 must pass.

As understood, HRSG 122 is operably coupled to exhaust passage 120 ofgas turbine 116 for generating steam for a steam turbine 124 (shownschematically in phantom in FIG. 3). HRSG 122 may include any now knownor later developed steam generating heat exchanger. As understood in theart, HRSG 122 may include a number of sets of heating pipes 150 throughwhich water and/or steam is passed to form steam or further heat steam.For example, HRSG 122 may include sets of pipes 150 that function asconventional parts of an HRSG such as but not limited to:superheater(s), economizer(s) and reheat section(s) for any number ofsteam turbine stages (i.e., HP, IP and/or LP). Any conventional steam orboiler drums (not shown) may also be provided relative to HRSG 122. HRSG122 may also include any necessary piping or valving (not shown) todeliver water/steam, as necessary. HRSG 122 may also include bypasssystems, valves, and attemperators to operate in rapid response mode.

HRSG 122 may also include conventional carbon monoxide (CO) catalystfilter 152 downstream of a first set of heat exchange pipes 150A. COcatalyst filter 152 may include any now known or later developed COcatalytic material capable of carrying out the desired catalyticconversion of CO to carbon dioxide (CO₂) or other less toxic pollutantsin a conventional manner. HRSG 122 may also include a conventionalselective catalytic reduction (SCR) system 154. As understood in theart, SCR system 154 converts NOx to nitrogen, water and carbon dioxideby causing the exhaust to react with a reducing agent, e.g., anhydrousammonia, aqueous ammonia or urea. SCR system 154 may include aconventional SCR filter 160 and an SCR reducing agent injector 162(e.g., an ammonia injection grid (AIG)) upstream of filter 160. SCRfilter 160 may include, for example, metal oxide or zeolite based porouscatalyst (e.g., V205/TiO₂). HRSG 122 may also have a combined SCR-COcatalyst instead of two separate catalysts. SCR reducing agent injector162 may include any now known or later developed injector system such asan array of nozzles, sprayers, etc., capable of coating SCR filter 160with reducing agent. SCR reducing agent injector 162 may be coupled toany form of reductant delivery system 164 including, for example, areductant reservoir 166, a reductant pump 168, control valve(s) 170,evaporator 172, heaters 174 and an air compressor 176 for delivery of anair flow to entrain reducing agent therein. Any now known or laterdeveloped power plant controller 180 may be employed to control theafore-described components.

FIG. 3 also shows an emission reduction system 200 (hereinafter “ERsystem 200”) for power plant 110 according to one embodiment of thedisclosure. ER system 200 includes an emission filter 202, and aretraction system 204. As used herein, “emission filter” indicates allor part of any form of exhaust toxin removing or reducing system. Aswill be described, the emission filter can remove different forms oftoxins and take on a variety of structural forms.

As shown in FIG. 3, in one embodiment, emission filter 202 takes theform of an SCR filter 206 of an SCR system 210 sized for a firstlocation 212 within exhaust passage 120. More specifically, emissionfilter 202 may include any now known or later developed filter mediumused for SCR. For example, SCR filter 206 may include a metal oxide orzeolite based porous catalyst (e.g., V205/TiO₂). As indicated, firstlocation 212 is upstream of HRSG 122, and emission filter 202 (SCRfilter 206) spans exhaust passage 120 and thus the exhaust path.Emission filter 202 may be smaller than conventional SCR filter 160 inHRSG 122 due to the size of exhaust passage 120 just downstream of gasturbine 116 compared to HRSG 122. In this embodiment, SCR system 210 mayalso include an SCR reducing agent injector 220, which may include anynow known or later developed injector system such as an array ofnozzles, sprayers, etc., capable of coating SCR filter 216 with reducingagent. As indicated, SCR reducing agent injector 220 is upstream offirst location 212 of the exhaust passage. In one embodiment, SCRreducing agent injector 220 may be permanently mounted within exhaustpassage 120, e.g., it includes metal piping and nozzles capable ofwithstanding the higher load temperatures of gas turbine 116. SCRreducing agent injector 220 may be coupled to any form of reducing agentdelivery system. In the example shown, SCR reducing agent injector 220is provided as an add-on to reductant delivery system 164. In this case,SCR reducing agent injector 220 is operatively coupled, e.g., via valves222 and conduits (not numbered), to reductant delivery system 164. Asexplained, reductant delivery system 164 includes reductant reservoir166, reductant pump 168, control valve(s) 170, evaporator 172, heaters174 and air compressor 176 for delivery of an air flow to entrainreducing agent therein. In alternative embodiments, SCR reducing agentinjector 220 may be coupled to its own standalone, and smaller, reducingagent delivery system, which would be structured similarly to system 164without coupling to parts in HRSG 122. In any event, as will bedescribed further herein, controller 180 can be modified, e.g., viahardware and/or software modifications, to control valve 222 thatdelivers reducing agent to injector 220. In operation, the reducingagent is injected onto SCR filter 206, and exhaust 118 passes throughthe SCR filter. As exhaust 118 passes through, the NOx reacts with thereducing agent and reduces NOx to nitrogen, water and carbon dioxide,which then may be exhausted to atmosphere or otherwise used for heatrecovery in a conventional manner downstream of ER system 200.

ER system 200 may also include a flow distributor 224 prior to emissionfilter 202 to distribute the exhaust flow properly and avoid exhaustflow bypass, which may be an issue during startup or low load conditionsas the flow coming into ER system 200 is approximately 5-20% of thedesign flow and the exhaust velocity profile may not be uniform. Flowdistributor 224 may include a perforated disc or some other design todistribute the flow properly, e.g., uniformly. Such flow distributor 224is only shown relative to FIG. 3 for clarity, but it can also be part ofany ER system arrangement described herein.

In another embodiment, shown in FIG. 4, emission filter 202 may take theform of a carbon monoxide (CO) catalyst filter 238 through which exhaust118 passes to remove carbon monoxide (CO) from exhaust 118 of gasturbine 116. As illustrated, CO catalyst filter 238 is positionedupstream of HRSG 122, which is operably coupled to exhaust passage 120of gas turbine 116 for generating steam for a steam turbine. CO catalystfilter 152 may include any now known or later developed CO catalyticmaterial capable of carrying out the desired catalytic conversion of COto carbon dioxide (CO₂) or other less toxic pollutants in a conventionalmanner. In one example, CO catalyst filter 238 may include a ceramicmonolith (e.g., FeCrAl) in a honeycomb arrangement coated with: awashcoat including, for example, aluminum oxide, titanium dioxide,silicon dioxide, and/or silica with alumina, etc.; ceria orceria-zirconia; and a catalyst such as but not limited to platinum,palladium, rhodium, cerium, iron, manganese and/or nickel. CO catalystfilter 238 can be a two-way or a three-way converter. In operation,exhaust 118 passes through CO catalyst filter 238 in which carbonmonoxide is converted to carbon dioxide in a conventional manner.Exhaust 118 may then be exhausted to atmosphere or otherwise used forheat recovery in a conventional manner downstream of ER system 200.

In another embodiment, shown in FIG. 3, emission filter 202 may take theform of a combined SCR/CO catalyst filter 242. In this embodiment,emission filter 202 includes both SCR filter layers and CO catalystfilter layers, and is functional to remove both NOx and CO. As will bedescribed herein (FIG. 9), in other embodiments, both an SCR system 210and a CO catalyst filter 238 may be provided upstream of HRSG 122.

Continuing with FIGS. 3 and 4, retraction system 204 is operably coupledto exhaust passage 120 of gas turbine 116, and is operable toselectively move emission filter 202 between first location 212 withinthe exhaust path and a second location 230 out of the exhaust path. Inthis fashion, as will be described in greater detail herein, ER system200 can temporarily position emission filter 202 just downstream of gasturbine 116 exhaust outlet and/or upstream of HRSG 122, for emissionreduction at low loads or startup conditions, and remove the emissionfilter 202 once operations move to higher loads and/or when the exhausttemperature exceeds the design temperature of emission filter 202 (e.g.,the temperature range for an illustrative SCR catalyst may be 176° C. to398° C. (i.e., 350° F.-750° F.), with some SCR materials capable of useup to 480° C. (i.e., approximately 900° F.) and in extreme cases up to537° C. (i.e., ˜1000° F.)). The second location 230, as will bedescribed, can be within exhaust passage 120 or outside of exhaustpassage 120, but is in either event, outside of the exhaust path.

Emission filter 202 and retraction system 204 can take a variety ofdifferent forms.

In the FIG. 3 embodiment, and as better illustrated in FIGS. 5-8,emission filter 202 may include a series of pivotally coupled panels240A-E. Any number of panels 240 may be employed in this fashion, e.g.,2, 3, 4 . . . 10, etc. In this embodiment, emission filter 202 mayresemble a vertically retractable garage door. As shown best in FIGS.5-6, in one embodiment, each panel 240A-E may include an open structureframe 250 (FIG. 6) having a filter medium 252 (FIG. 5) therein throughwhich exhaust 118 passes. Open structure frame 250 may have any shape orsize desirable for the particular gas turbine 116 to which attached andparticular toxin to be removed. Filter medium 252 may include any filtermaterial as appropriate for the type of toxin to be removed, e.g., acarbon monoxide (CO) catalyst filter and/or an SCR filter. Each panel240A-E may have any requisite thickness for the desired emissionreduction being carried out thereby. In one example, each panel 240A-Ehas a thickness of less than 0.6 meters. In one embodiment, shown inFIG. 5, each panel 240A-E is pivotally coupled to at least one adjacentpanel by hinges 254. Hinges 254 may take the form of any hinge capableof withstanding the environmental conditions within exhaust passage 120and structurally pivotally supporting panels 240A-E. Any number ofhinges 254, e.g., 1, 2, 3, etc., necessary may be employed between pairsof panels 240A-E. In other embodiments, other mechanisms for pivotallycoupling panels 240A-E may be employed including but not limited to:lengths of looped material 256 (FIG. 6) such as metal cable, chains,etc.; and arced members (not shown) extending from one panel and seatingin an adjacent panel. Open structure frame 250 may be made of anymaterial capable of providing structural support and withstanding theenvironmental conditions within exhaust passage 120, e.g., high thermalresistance metal or metal alloys. As shown in FIG. 6 only, each openstructure frame 250 may include a movable closure 258 selectivelyclosing an access opening 260 to an interior of frame 250, and allowingaccess to the access opening. Movable closure 258 may take the form ofany sort of movable closure such as but not limited to: a pivoting door(shown), slide door, and a bolted on cover. Each filter medium 252 maybe replaceable, and may be replaced through access opening 260. It isnoted that in FIG. 6, emission filter 202 is shown in a curved, expandedarrangement to illustrate its components' size and shape. In operation,as shown in FIGS. 7-8, panels 240A-E may stack vertically so as to forma filter wall through which exhaust 118 must pass to move downstream inexhaust passage 120.

As also shown in FIG. 6, a flexible mesh 262 may cover at least aportion of an exterior of panels 240A-C to protect filter medium 252therein. Flexible mesh 262 can be any form of mesh that exhaust can passthrough but will protect filter medium 252, e.g., flexible metalscreening, chainmail, etc. Flexible mesh 262 must also be able towithstand the environmental conditions within exhaust passage 120.Flexible mesh 262 may cover panels 260A-C collectively or individually,and is preferably replaceable.

In one embodiment, shown in FIGS. 5, 7 and 8, each panel 240A-E may havea pair of opposing bearings 268 extending from opposing ends of therespective panel. In this case, retraction system 204 may include a pairof bearing tracks 260A, 260B configured to receive a bearing 268 of aselected opposing end of pair of opposing bearings of panels 240A-E.That is, bearing 268 is configured to mate with a track system 260A,260B, which in turn direct positioning of emission filter 202. As shownin FIGS. 7 and 8, pair of bearing tracks 260A, 260B each include a firstportion 263 arranged to position emission filter 202 at first location212 in exhaust passage 120 in response to bearings 268 being in firstportion 263. Further, pair of bearing tracks 260A, 260B each include asecond portion 264 arranged to position emission filter 202 at secondlocation 230 in response to bearings 268 being in second portion 264.Also, pair of bearing tracks 260A, 260B each include a transitionportion 266 coupling first portion 263 and second portion 264. In thisfashion, as bearings 268 move along tracks 260A, 260B, emission filter202 can be moved from first location 212 to second location 230. Bearingtracks 260A, 260B can take any form capable of receiving and/or holdingbearings 268, e.g., L-shaped, U-shaped, U-shaped with rounded ends, etc.

An actuator 270 is configured to move emission filter 202 along pair ofbearing tracks 260A, 260B. Actuator 270 may include any form ofmotorized system capable of moving emission filter 202 along tracks260A, 260B. In one example, actuator 270 may include an electric,hydraulic or pneumatic motor 272 coupled to an uppermost panel 240D ofemission filter 202 by a transmission linkage 274 (e.g., a chain, cable,etc.). Transmission linkage 274 may take a variety of forms such as butnot limited to: a length of material reeled onto/off of a reel coupledto motor 372, a band of chain positioned about a pair of gears, onecoupled to motor 272, and coupled to emission filter 202. Activation ofmotor 272 in one direction moves emission filter 202 from first location212 to second location 230, and activation of motor 272 in the oppositedirection moves emission filter 202 from second location 230 to firstlocation 212. In FIGS. 7 and 8, motor 272 of actuator 270 may be withinfilter enclosure 290 (FIG. 7) or outside of exhaust passage 120 andfilter enclosure 290 (FIG. 8). When outside of filter enclosure 290, anyform of transmission 291 (FIG. 8), e.g., a drive shaft, gear box, drivechain, etc., can extend into enclosure 290, as necessary. Theabove-described retraction system 204 may be varied in a wide variety ofways including but not limited to: more or less tracks, differenttransmission, different actuator motor, etc. As will be describedfurther, actuator 270 is controlled by controller 180.

In one embodiment, shown in FIG. 7, second location 230 is outside ofexhaust passage 120. In this case, exhaust passage 120 may include anopening 280 configured to permit movement of emission filter 202therethrough to an outside of exhaust passage 120. Opening 280 may beprovided, for example, within a wall 282 of exhaust passage 120. In theexample shown, wall 282 includes an upper wall of exhaust passage 120,but it may be any wall of exhaust passage 120. Opening 280 may beconfigured to be selectively openable or closable with an automatedclosure 284, e.g., a pivoting door, slidable door, etc., under controlof controller 180. In addition, opening 280 may be configured to allowtracks 260A, 260B to pass therethrough. When opening 280 is open,emission filter 202 may pass therethrough, and when closed, emissionfilter 202 cannot pass therethrough and exhaust passage 120 is closed tothe environment. Any form of atmospheric enclosure 286 may be providedto close off exhaust passage 120 from the outside environment whenopening 280 is open.

Some emission filters 202, e.g., SCR filters, should not be exposed toatmosphere or environments that expose them to substances that maynegatively impact their ability to function, e.g., dust, high or lowmoisture and/or other atmospheric conditions. To this end, as shown inFIG. 7, an emission filter enclosure 290 may be provided outside exhaustpassage 120. In this case, in second location 230, emission filter 202is positioned within emission filter enclosure 290. Emission filterenclosure 290 can include any form of compartment capable of preventingexposure of emission filter 202 to the undesired conditions, e.g., dust,moisture, etc. Emission filter enclosure 290 can be, for example, a hardsurfaced box, e.g., plastic or metal; a flexible compartment, e.g., bag.While shown positioned against wall 282 of exhaust passage 120,enclosure 290 can be spaced from exhaust passage 120.

In another embodiment, shown in FIG. 8, second location 230 is inside ofexhaust passage 120, but outside of the exhaust path. In this case,tracks 260A, 260B provide second location 230 at a position outside ofthe exhaust path but still within exhaust passage 120. Although insideof exhaust passage 120, some emission filters 202 should not be exposedto the higher load conditions of exhaust 118, e.g., higher temperatures,etc. To this end, as shown in FIG. 8, an emission filter enclosure 292may be provided inside exhaust passage 120. In second location 230 inFIG. 8, emission filter 202 is positioned within emission filterenclosure 292 inside exhaust passage 120. Emission filter enclosure 292can include any form of compartment capable of preventing exposure ofemission filter 202 to the undesired conditions, e.g., hightemperatures, within exhaust passage 120. Emission filter enclosure 292can be, for example, a hard surfaced box, e.g., metal. While shownpositioned against wall 282 of exhaust passage 120, enclosure 292 can bespaced from any wall of exhaust passage 120. To protect emission filter202 during higher load conditions, emission filter enclosure 292 mayinclude a closable opening 294 configured to permit movement of emissionfilter 202 therethrough when open. Opening 294 may be configured to beselectively openable or closable with an automated closure 297, e.g., apivoting door, slidable door, etc., under control of controller 180. Inaddition, opening 294 may be configured to allow tracks 260A, 260B topass therethrough. When opening 294 is open, emission filter 202 maypass therethrough, and when closed, emission filter 202 cannot passtherethrough and is, when inside of enclosure 292, protected fromconditions within exhaust passage 120. In this embodiment, motor 272 ofactuator 270 may be within or, as shown in, outside of exhaust passage120 and filter enclosure 292. When outside of exhaust passage 120, anyform of transmission 291, e.g., a drive shaft, gear box, drive chain,etc., can extend into enclosure 292, as necessary.

With reference to FIGS. 6 and 9, in another embodiment, a retractionsystem 204A may include an actuator 270 as in previously-describedembodiments, but rather than a track system 260A, 260B, a ramp 296capable of directing emission filter 202 to second location 230 isprovided. Ramp 296 may be formed as a single planar element that alsofunctions as an enclosure 298. Ramp 296 and actuator 270 may be outsideof exhaust passage 120. A selectively openable opening 299 may beprovided in exhaust passage 120 to allow for selective movement ofemission filter 202 between first location 212 and second location 230(in phantom). Ramp 296 includes a curved portion 301 allowing fordropping of panels 240A-E of emission filter 202 to first location 212in a stacked manner. Any form of guide elements (not shown) necessary toensure proper positioning and movement of emission filter 202 may beapplied.

FIG. 9 also shows an optional embodiment in which emission filter 202includes an SCR system 210 including an SCR filter 206 and a carbonmonoxide (CO) catalyst filter 238 upstream of SCR filter 206. Both SCRfilter 206 and CO catalyst filter 238 are upstream of HRSG 122. Both SCRfilter 206 and CO catalyst filter 238 can be retractably mounted totheir own respective retraction system 204A, 204B. Retraction system204B can take any form described herein. In the example shown,retraction system 204B is similar to retraction system 204 in FIG. 8,inside of exhaust passage 120.

Referring to FIGS. 10-14, in another embodiment, ER system 200 for powerplant 110 including gas turbine 116 may include an emission filter 302including a first panel 340 and a second panel 342. Panels 340, 342 mayeach include an SCR filter for SCR system 210, as shown in FIG. 10, a COcatalyst filter (like in FIG. 6) or a combination SCR and CO filter. Inthis embodiment, panels 340, 342 slide in from a side of exhaust passage120 rather than on a vertically oriented track as in FIGS. 3-9. Eachpanel 340, 342 may be constructed similarly to panels 240A-E (FIG. 6),and may include an open structure frame 250 having filter medium 252therein through which exhaust 118 passes to remove an exhaust componentof the exhaust of gas turbine 116. In contrast to pivotally coupledpanels 240A-E, each panel 340, 342 are moved laterally into place andare sized so as to cover a large portion of the cross-section of exhaustpassage 120. As shown in FIG. 11, each panel 340, 342 may take up, forexample, 50% of the cross-sectional area of exhaust passage 120, but inany event collectively cover the cross-sectional area so as to cross theexhaust path. Each panel 340, 342 may have any thickness (along exhaustpath) necessary to provide the desired emission reduction, e.g., lessthan 0.6 m thick.

A retraction system 304 is operably coupled to exhaust passage 120 ofgas turbine 116 to move panels 340, 342. In this embodiment, retractionsystem 304 may selectively laterally move each of first and secondpanels 340, 342 between first location 212 within the exhaust pathwithin exhaust passage 120 and a second location 230 out of the exhaustpath, e.g., under control of controller 180. Retraction system 304 mayinclude any variety of structures capable of laterally moving panels340, 342 between first location 212 and second location 230 in anautomated fashion. In one embodiment, shown in FIGS. 11-13, retractionsystem 304 may include a first and second bearing track 350, 352configured to guide movement of panels 340, 342. First bearing track 350extends laterally from within exhaust passage 120 through a first sideopening 356 in exhaust passage 120, and is configured to receive (e.g.,sized and shaped) first panel 340 to allow lateral movement of the paneltherein. As shown in FIG. 14, first side opening 356 is configured(e.g., sized and shaped) to permit movement of first panel 340therethrough. Similarly, as shown in FIGS. 11-13, second bearing track352 extends laterally from within exhaust passage 120 through a secondside opening 358 in exhaust passage 120, and is configured to receivesecond panel 342 to allow lateral movement of the pane therein. Secondside opening 358 (FIG. 11) is configured to permit movement of thesecond panel therethrough, similarly to opening 356 in FIG. 14.

As best illustrated in FIG. 14 for bearing track 350, in the embodimentshown, each bearing track 350 (and 352 in FIGS. 11-13) may include apair of vertically spaced track elements 360, 362 (FIG. 14 only) thatextend laterally into exhaust passage 120 to allow movement of arespective panel, e.g., 340, therealong between first location 212 (FIG.11) and second location 230. Each track element 360, 362 extending fromone side of exhaust passage 120 may be integral with its correspondingtrack element extending from the other side of exhaust passage 120 (for352 in FIGS. 11-13), so each upper and lower track elements 360, 362 areone piece. However, they may also be four separate track elements. Inthe example shown, track elements 360, 362 include U-shaped elements,but any element capable of laterally guiding a respective panel may beprovided. In the example shown, each panel 340, 342 may include one ormore bearings 364 for engaging a respective bearing track 350, 352, and,more particularly, engaging a respective track element 360, 362, forallowing the panels to move laterally guided by track elements 360, 362.In one example, as shown in in FIG. 14, bearings 364 may include aplurality of wheels 366 for rolling engagement with each track element360, 362 (like heavy sliding glass doors). Other bearing mechanisms forallowing movement may also be provided such as skids or rolling tracks.In another embodiment, a bearing 364 may be provided on only the top orbottom of a respective panel. For example, bearing 364 may include slideor roller bearings engaging a horizontal track on an upper track element360 with no load-carrying bearings provided for the lower track element,or non-load-carrying bearings may be provided on the lower track element362 for guidance only (like a glass shower door or sliding hangingcloset doors).

ER system 200 may also include an actuator 370 configured to move eachof the first and second panels 340, 342 between first location 212within the exhaust path within exhaust passage 120 and second location230 laterally outside of the exhaust passage. Actuator 370 can take avariety of forms. In one embodiment, shown best in FIG. 14, actuator 370may include a linkage 368 to a motor 372 that forces movement of panels340, 342 along track elements 360 and/or 362, e.g., such as a loop ofchain movable by motor 372 and coupled to panel 340 or 342. There are alarge variety of actuators capable of providing this sort of movement,all of which are considered within the scope of the disclosure. In oneembodiment, shown in FIG. 14, actuator 370 is similar to a garage dooractuator, e.g., a motor under control of controller 180 and a chainconfigured to move panels 340, 342 along track element(s) 360, 362; or amotor having a rotating gear that meshes with a pinion gear on thepanels 340, 342 (see FIGS. 18-19); etc. More than one motor may beemployed, e.g., one on each side of exhaust passage 120, as may benecessary.

As shown best in FIG. 14, side opening 356 (and side opening 358 inFIGS. 11-13) may include a closure 376 therefor. Closures 376 mayinclude any form of automated closing element, e.g., a sliding closure,pivoting door, etc., controllable by controller 180 and capable ofsealing exhaust passage 120 from outside when emission filter 302 is notin use.

As shown in FIG. 14, in one optional embodiment, ER system 200 mayfurther include a first panel enclosure 380 configured to receive firstpanel 340 in second location 230. As shown, first panel enclosure 380couples to exhaust passage 120 and covers first side opening 356. Asshown in FIG. 12, a second panel enclosure 382 is configured to receivesecond panel 342 in second location 230. Second panel enclosure 382 iscoupled to exhaust passage 120 and covers second side opening 358 (FIG.11). Each enclosure 380, 382 may include a closure for closing anopening therein through which a respective panel enters the enclosure.In the example in FIG. 14, closure 376 may provide dual purpose ofclosing side openings 356, 358 (FIG. 11) of exhaust passage 120 andclosing enclosure(s) 380, 382. Alternatively, each enclosure 380, 382may include its own dedicated automated closure.

Referring to FIGS. 13 and 14, ER system 200 may also include a firstpivot element 390 coupled to first panel 340 and a second pivot element392 coupled to second panel 342, e.g., between panels 340, 342 andrespective bearings 364. Each pivot element 390, 392 may permit pivotingof a respective panel from second location 230 to a storage location 232adjacent an exterior side 394 of exhaust passage 120. Track elements360, 362 may include cutouts 377 or other mechanisms for allowingpivoting movement of a respective panel to storage location 232 awayfrom track elements 360, 362. In this fashion, each panel 340, 342 canbe laterally moved out of exhaust passage 120 and out of the wayadjacent to exhaust passage 120, lowering the size of the footprint ofER system 200. Any form of motorization to power the pivoting can beprovided. In one embodiment, shown in FIG. 14, panel enclosures 380, 382(FIG. 12) may be configured to receive a respective panel 340, 342 andbe movable to storage location 232 therewith. In this case, pivotelements 390 for panels 340, 342 may be omitted, and each enclosure 380,382 may include a pivot element 396 allowing collectively pivoting ofthe enclosure and panel therein to storage location 232.

Referring to FIGS. 15-18, ER system 200 for power plant 110 includinggas turbine 116 according to another embodiment is illustrated. In thisembodiment, an emission filter 402 includes a single panel similar instructure to panels 240A-E (FIGS. 6-8) and panels 340, 342 (FIG. 14),but sized to extend across a cross-sectional area of exhaust passage 120so as to cover all of the exhaust path. In the example shown, emissionfilter 402 selectively moves vertically between first location 212 andsecond location 230. As shown in FIG. 17, emission filter 402 mayinclude, as with previous embodiments, an open structure frame 250having filter medium 252 therein through which exhaust 118 passes toremove an exhaust component of the exhaust of the gas turbine. As inpreviously described embodiments, emission filter 402 may include an SCRfilter for SCR system 210, as shown in FIG. 15, a CO catalyst filter(like in FIG. 6) or a combination SCR and CO filter.

Retraction system 404 is operably coupled to exhaust passage 120 of gasturbine 116. In this embodiment, retraction system 404 selectivelyvertically moves emission filter 402 through an opening 456 in an upperwall 458 of exhaust passage 120 between first location 212 within theexhaust path within the exhaust passage and a second location 230 out ofthe exhaust path. As shown best in FIG. 16, opening 456 may include aclosure 476 therefor. Closure 476 may include any form of automatedclosing element, e.g., a sliding closure, pivoting door, etc.,controllable by controller 180 and capable of sealing exhaust passage120 from outside when emission filter 402 is not in use.

Retraction system 404 may take a variety of forms. In one example, shownin FIGS. 16 and 17, retraction system 404 is similar to that shown inFIG. 14, except it is set vertically and moves emission filter 402vertically instead of horizontally. Here, retraction system 404 mayinclude a first bearing track 450 extending vertically from withinexhaust passage 120 through opening 456 (in upper wall 458) in exhaustpassage 120. Bearing track 450 is configured (e.g., sized and shaped) todirect a first side 460 of emission filter 402 through opening 456.Similarly, retraction system 404 may include a second bearing track 452extending vertically from within exhaust passage 120 through opening 456in the exhaust passage and configured to direct a second side 462 of theemission filter 402 through opening 456. In the example shown, bearingtracks 450, 452 include U-shaped elements, but any element capable oflaterally guiding emission filter 402 may be provided. In the exampleshown, emission filter 402 may not include any bearings thereon, but asdescribed relative to panels 340, 342 (FIG. 14), emission filter 402 mayinclude one or more bearings for engaging a respective bearing track450, 452, if necessary, for vertically guided movement. Any bearingmechanisms for allowing movement may be provided such as:rollers/wheels, skids or rolling tracks.

ER system 200 according to the FIGS. 15-17 embodiments may also includean actuator 470 configured to move emission filter 402 between firstlocation 212 within the exhaust path within exhaust passage 120 andsecond location 230 vertically outside of the exhaust passage. Actuator470 can take a variety of forms. In one embodiment, shown best in FIGS.16-17, actuator 470 may include a linkage 468 to a motor 472 that forcesmovement of emission filter 402 along bearing tracks 450, 452, e.g.,such as a loop of chain movable by motor 472 and coupled to panel 340 or342. There are a large variety of actuators capable of providing thissort of movement, all of which are considered within the scope of thedisclosure. In one embodiment, shown in FIG. 17 actuator 470 is similarto a garage door actuator, e.g., a motor under control of controller 180and a chain configured to move emission filter 402 along bearing tracks450, 452. In another embodiment, shown in FIGS. 18 and 19, actuator 470may include a motor(s) 478 having a rotating gear 480 that meshes with apinion gear(s) 482 on one or both sides of emission filter 404 to raiseand lower the emission filter. This sort of rack-and-pinion actuator canalso be applied to the side entry embodiments such as shown in FIG. 14.

ER system 200 according to this embodiment may also include, as shown inFIGS. 16-19, a pivot element 490 coupled to emission filter 402. Asshown best in FIGS. 16 and 19, pivot element 490 permits pivoting ofemission filter 402 from second location 230 to a storage location 232in which emission filter 402 is positioned adjacent an upper, exteriorside 492 of exhaust passage 120. Pivoting of emission filter 402 may becontrolled by a motor 494 coupled to pivot element 490, outside ofexhaust passage 120.

As shown in FIG. 15, a filter enclosure 500 configured to receiveemission filter 402 in second location 230 and movable to storagelocation 232 may also be provided. As in previous embodiments, filterenclosure 500 may include a closure 502 for closing an opening thereinthrough which emission filter 402 enters the filter enclosure.

FIG. 20 shows an alternative embodiment that is similar to those inFIGS. 15-19. In this embodiment, however, emission filter 402 extendsacross only a portion of the exhaust path in first location 212, e.g.,30-70%. That is, emission filter 402 does not cover an entirecross-sectional area of exhaust passage 120. In this embodiment, adamper 510 may be selectively movable between an operative location 512in which the damper extends across a remaining portion of the exhaustpath not covered by emission filter 402, and a retracted position 514outside of the exhaust path. In this embodiment, a smaller emissionfilter 402 can be employed and damper 510 can act to control the exhaustpath to force exhaust 118 through the emission filter 402. In theretracted position, damper 510 is substantially out of the exhaust pathso as to provide no resistance to exhaust 118 passing through exhaustpassage 120. In one particular example, emission filter 402 may includea CO catalyst filter that extends across only a portion of the exhaustpath in first location 212, and damper 510 is selectively movablebetween an operative location 512 in which the damper extends across aremaining portion of the exhaust path not covered by the CO catalystfilter and retracted position 514 outside of the exhaust path. Damper510 can be pivotably mounted or slidably mounted, and can include anyappropriate mechanism to control moving thereof, e.g., a hydraulic ram,motor, etc. Retraction system 404 operates similarly to describedrelative to FIGS. 15-19.

Controller 180 is operably coupled to retraction system 204, 304, 404and is configured to instruct retraction system 204, 304, 404 to moveemission filter 202, 302, 402 between first location 212 and secondlocation 230 in response to an emission condition of exhaust 118 fromgas turbine 116. Controller 180 may move the emission filter regardlessof the embodiment employed herein, e.g., panels 240A-E (FIGS. 7-8),panels 340, 342 (FIGS. 10-14) or single panel emission filter 402 (FIGS.15-20). Controller 180 may be part of a larger power plant controlsystem (not shown) or may be a separate entity that cooperates with alarger power plant control system. In any event, controller 180, viahardware and/or software, controls any retraction system(s) describedherein and controls any ancillary equipment necessary to operate of ERsystem 200 such as but not limited to control valve 222 (e.g., FIG. 3)of any SCR system 210 employed that delivers reducing agent to injector220. In one embodiment, first location 212 at which emission filter 202,302, 402 may be employed is selected to provide the best possibleemission filtering for the toxin to be reduced at the emissioncondition(s) at the anticipated plant low load conditions. While notlimited to startup or low load conditions, ER system 200 is particularlyadvantageous during such load conditions during which certain toxinssuch as carbon monoxide (CO) or nitrous dioxide are high butconventional emission filtering equipment (i.e., those downstream ofheat exchange piping in HRSG 122) is not operational. Low loadconditions may include, for example, loads of less than 15% of the fullload of gas turbine 116 or combined cycle power plant 10. To this end,first location 212 may be selected to be close enough to turbine 116that emission condition(s) is/are sufficient to ensure operation ofemission filter 202, 302, 402 during the desired loads.

Emission condition(s) may include any number of exhaust conditions orcombinations thereof. For example, a certain exhaust temperature may benecessary for certain emission filters, e.g., SCR filter 206, tooperate. Further, operation of ER system 200 according to embodiments ofthe disclosure may not be desired unless certain exhaust component(s)(e.g., CO₂, CO or NOx, etc.) level(s) are high. To this end, ER system200 may include any number of emission condition sensors 300 operativeto sense one or more emission conditions such as at least one of anexhaust temperature of exhaust 118, and at least one exhaust componentlevel. While certain emission sensors 300 are shown, it is emphasizedthat others may also be provided, wherever necessary. The emissionconditions can be raw data as measured by a particular sensor 300 or maybe interpolated data such as an emission component amount per hour beingexhausted to atmosphere based on an emission component level withinexhaust 118 as measured by a particular sensor 300 and an exhaust rateflow, turbine load or other parameter indicative of exhaust flow. Suchinterpolations are well known determinations made by controller 180, andcan be made in any now known or later developed fashion. ER system 200may also include any other necessary sensors now known or laterdeveloped such as but not limited to position sensors to determineemission filter 202, 302, 402, closure or damper locations.

In operation, according to one embodiment, controller 180 may instructretraction system 204, 304, 404 to move emission filter 202, 302, 402 tofirst location 212 in response to the exhaust temperature of exhaust 118being within a predetermined temperature range, i.e., as measured by anappropriate temperature sensor (sensors 300). In one embodiment, thepredetermined temperature range may between 398° Celsius and 537°Celsius (i.e., 750-1000° Fahrenheit); however, the range may vary basedon many factors such as turbine 116 size, expected emission componentsrequiring reduction, etc. Further, controller 180 may instructretraction system 204, 304, 404 to move emission filter 202, 302, 402 tosecond location 230, out of the exhaust path, in response to the exhausttemperature being outside the predetermined temperature range, e.g.,higher than 398° C.

In another embodiment, controller 180 may instruct retraction system204, 304, 404 to move emission filter 202, 302, 402 to first location212 in response to at least one exhaust component level exceeding arespective exhaust component limit. For example, the exhaust componentmay be CO having a level greater than 2.0 parts per million as measuredby a sensor(s) 300 that measures CO content, and/or may be NOx having alevel that equates to greater than 19 kilograms per hour being exhaustedto atmosphere as measured by a sensor(s) 300 that measure NOx content.Further, controller 180 may instruct retraction system 204, 304, 404 tomove emission filter 202, 302, 402 to second location 230 in response tothe at least one exhaust component level not exceeding the respectiveexhaust component limit. Once a load and other conditions that indicatethe operativeness of ER system 200 is no longer necessary or possible,e.g., exhaust temperature has reach greater than 398° C., retractionsystem 204, 304, 404 can retract emission filter 202, 302, 402 to secondlocation 230. Here, conventional emission reduction systems such as COcatalyst filter 152 and/or SCR system 154 in HRSG 122 are operational.

It is understood that emission filter 202, 302, 402 can be configured inany number of ways to provide the functionality herein. Each filter 202,302, 402, in an operative state, may extend up to, for example, 30meters, and have a thickness less than approximately 0.6 meters.

The foregoing drawings show some of the processing associated accordingto several embodiments of this disclosure. It should also be noted thatin some alternative implementations, the acts described may occur out ofthe order noted or, for example, may in fact be executed substantiallyconcurrently or in the reverse order, depending upon the act involved.Also, one of ordinary skill in the art will recognize that additionalsteps that describe the processing may be added.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. “Optional” or “optionally” means thatthe subsequently described event or circumstance may or may not occur,and that the description includes instances where the event occurs andinstances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged, such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.“Approximately” as applied to a particular value of a range applies toboth values, and unless otherwise dependent on the precision of theinstrument measuring the value, may indicate +/−10% of the statedvalue(s).

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. An emission reduction system for a power plantincluding a gas turbine, the system comprising: an emission filter; aretraction system operably coupled to an exhaust passage of the gasturbine, the exhaust passage defining an exhaust path of exhaust fromthe gas turbine, the retraction system selectively moving the emissionfilter between a first location within the exhaust path and a secondlocation outside of the exhaust path; and a controller operably coupledto the retraction system configured to instruct the retraction system tomove the emission filter between the first location and the secondlocation in response to an emission condition of the exhaust from thegas turbine, wherein the emission condition includes an exhausttemperature of the exhaust, and wherein the controller instructs theretraction system to move the emission filter to the first location inresponse to the exhaust temperature of the exhaust being within apredetermined temperature range, and instructs the retraction system tomove the emission filter to the second location in response to theexhaust temperature being outside the predetermined temperature range.2. The emission reduction system of claim 1, wherein the power plantfurther includes a heat recovery steam generator (HRSG) operably coupledto the exhaust passage of the gas turbine for generating steam for asteam turbine, and wherein the first location is upstream of the HRSG.3. The emission reduction system of claim 1, wherein the emissioncondition includes at least one exhaust component level.
 4. The emissionreduction system of claim 1, wherein the predetermined temperature rangeis between 398° Celsius and 537° Celsius.
 5. The emission reductionsystem of claim 3, wherein the controller instructs the retractionsystem to move the emission filter to the first location in response tothe at least one exhaust component level exceeding a respective exhaustcomponent limit, and instructs the retraction system to move theemission filter to the second location in response to the at least oneexhaust component level not exceeding the respective exhaust componentlimit.
 6. The emission reduction system of claim 1, wherein the emissionfilter includes a carbon monoxide (CO) catalyst filter.
 7. The emissionreduction system of claim 1, wherein the emission filter includes aselective catalytic reduction (SCR) filter, and further comprising anSCR reducing agent injector upstream of the first location of theexhaust passage.
 8. The emission reduction system of claim 7, furthercomprising a carbon monoxide (CO) catalyst filter downstream of the SCRfilter and upstream of a heat recovery steam generator (HRSG) operablycoupled to the exhaust passage of the gas turbine for generating steamfor a steam turbine.
 9. The emission reduction system of claim 1,wherein the emission filter includes a series of pivotally coupledpanels, each respective panel of the series of pivotally coupled panelsincluding an open structure frame having a filter medium therein throughwhich the exhaust passes and a pair of opposing bearings extending fromopposing ends of the respective panel.
 10. The emission reduction systemof claim 9, wherein the retraction system includes: a pair of bearingtracks, each track of the pair of bearing tracks configured to receive arespective bearing from one of the pairs of opposing bearings of theseries of pivotally coupled panels, the pair of bearing tracks eachincluding a first portion arranged to position the emission filter atthe first location in the exhaust passage in response to the respectivebearings being in the first portion, a second portion arranged toposition the emission filter at the second location in response to therespective hearings being in the second portion, and a transitionportion coupling the first portion and the second portion, and anactuator configured to move the emission filter along the pair ofbearing tracks.
 11. The emission reduction system of claim 1, furthercomprising an emission filter enclosure within the exhaust passage,wherein the second location positions the emission filter within theemission filter enclosure.
 12. The emission reduction system of claim 1,wherein the exhaust passage includes an opening configured to permitmovement of the emission filter therethrough to an outside of theexhaust passage, and further comprising an emission filter enclosureoutside of the exhaust passage, wherein the second location positionsthe emission filter within the emission filter enclosure.
 13. Theemission reduction system of claim 1, further comprising an exhaust flowdistributor upstream of the emission filter.
 14. A method of reducingemissions for a power plant including a gas turbine, the methodcomprising: providing an emission filter operably coupled to aretraction system that is operably coupled to an exhaust passage of thegas turbine, the exhaust passage defining an exhaust path of exhaustfrom the gas turbine; and selectively moving the emission filter, usingthe retraction system, between a first location within the exhaust pathand a second location outside of the exhaust path in response to anemission condition of the exhaust from the gas turbine, wherein theemission condition includes at least one of: an exhaust temperature ofthe exhaust and at least one exhaust component level, and wherein theselective moving includes moving the emission filter to the firstlocation in response to the exhaust temperature of the exhaust beingwithin a predetermined temperature range, and moving the emission filterto the second location in response to the exhaust temperature beingoutside the predetermined temperature range.
 15. The method of claim 14,wherein the power plant further includes a heat recovery steam generator(HRSG) operably coupled to the exhaust passage of the gas turbine forgenerating steam for a steam turbine, and wherein the first location isupstream of the HRSG.
 16. The method of claim 14, wherein the selectivemoving includes moving the emission filter to the first location inresponse to the at least one exhaust component level exceeding arespective exhaust component limit, and moving the emission filter tothe second location in response to the at least one exhaust componentlevel not exceeding the respective exhaust component limit.